Disordered superconductors: Third-harmonic response and charge fluctuations

本项目的科学目标是了解无序对铜酸盐超导体在以下方面的影响：(A)泵浦-探测实验的三次谐波响应中集体模的特征。在这里，我们计划研究d波超导体在无序影响下的相应光谱。特别是，我们感兴趣的是振幅模、电荷模和相位模对低能响应的贡献，同时我们还打算分析长程库仑相互作用的影响。我们的目的是解释实验观察到的铜酸盐超导体中三次谐波响应的极化相关性和相位，这与S波系统的预期结果有很大的不同。(B)电荷序波和电荷密度波的涨落结构。最近的实验表明，在相图的很大一部分中存在短程电荷涨落，这可能是奇怪金属相中不寻常的输运性质的原因。在本项目中，我们打算研究无序应变薄膜中这种涨落的结构，其中输运和RIXS实验揭示了向列相的基态。在这两个主题上，我们与罗马大学拉萨皮恩扎大学物理系固体理论小组进行了长期的合作，我们的目标是在本提案中继续下去。

The scientific aim of the present project is related to an understanding of the influence of disorder in cuprate superconductors with regard to the following aspects:(a) Signatures of collective modes in the third-harmonic response of pump-probe experiments. Here we are planning the investigation of the corresponding spectra for d-wave superconductors under the influence of disorder. In particular, we are interested in the contribution of amplitude- , charge and phase modes on the low energy response where we also intend to analyze the influence of long-range Coulomb interactions. We aim to explain the experimentally observed polarization dependence as well as the phase of the third harmonic response in cuprate superconductors which is substantially different from that expected for s-wave systems.(b) Structure of charge-order and charge density wave fluctuations. Recent experiments have revealed the presence of short-range charge fluctuations in a large part of the phase diagram which may account for the unusual transport properties in the strange metal phase. Within the present project we intend to study the structure of such fluctuations in disordered strained films where transport and RIXS experiments have revealed a nematic ground state.On both topics we have a long-standing cooperation with the Solid State Theory group of the Department of Physics at the University of Rome ’La Sapienza’ which we aim to continue within the present proposal.